The dry method such as sputtering, physical vapor deposition (PVD), chemical vapor deposition (CVD), and so on, and the wet method as typified by sol-gel method are known as techniques for forming a metal oxide film on a surface of glass, metal, ceramics and other substrates.
However, the dry process by the physics method such as sputtering, PVD and so on necessitates high degree of vacuum. Maintaining such high vacuum becomes more difficult as a device becomes larger. Therefore, forming a metal oxide film over a large dimension is difficult. Moreover, a large quantity of energy is required so as to vaporize the materials, and an enormous quantity of energy is additionally required since base plates, on which metal oxide films are formed, must be also heated so as to improve the quality of film formation. Furthermore, in a case wherein a base plate has a complex shape, film formation is difficult in a “shadow” portion of the base plate.
Still furthermore, CVD involves chemical reaction, which makes difficult to maintain uniform composition of a film and requires control of by-products. Therefore, extremely complicated control is required.
Also, in sol-gel method, since the progress of a condensation polymerization reaction is remarkably different depending on a temperature and humidity, strict control on film forming conditions becomes necessary in order to constantly obtain uniform films. Moreover, since the sol of a coating liquid is often unstable, there are many problems to be solved in an actual use, and some design is needed in order to maintain the viscosity of the sol and to prevent sedimentation of solid particles. Furthermore, there are cases in which exhibition of a specific function in a metal oxide film is desired by adding two or more kinds of metal species to a metal oxide film. In sol-gel method, however, since hydrolysis rate is different depending on the metal species, phase separation is caused even if dissimilar metals are mixed. Thus, it is unable to exhibit such a function.
Thus, a technique is proposed for applying a coating liquid including metal complexes to a surface of a metal plate, and thereafter firing to thermally decompose the metal complexes to form a metal oxide film (see Patent Documents 1-3). In this technique, multidentate ligands including two or more substituents such as an amino group, a hydroxyl group and others, like etylenediaminetetraacetate, diethanolamine, acetylacetone and so on, in the molecule are frequently used as ligands of metal complexes.    Patent Document 1: Unexamined Japanese Patent Publication No. 9-278489    Patent Document 2: Unexamined Japanese Patent Publication No. 11-228113    Patent Document 3: Unexamined Japanese Patent Publication No. 11-256342